Nest site selection by northern goshawk Accipiter gentilis in northern coastal birch forests

Abstract

Most studies of nest site selection by northern goshawk, Accipiter gentilis, have been done in mixed – or coniferous forests, and emphasis has been put on the importance of large trees and relatively intact, old forest stands for nesting sites. However, goshawks in northern Norway are found in birch forests characterized by relatively small trees and a high natural level of fragmentation. In this study nest site selection by goshawk was studied by measuring the forest and vegetation structure of selected nesting stands in northern coastal birch forests. Twenty two nesting sites and twenty two paired random sites were used. PCA was used to analyse the structural and vegetation variables. Non-centred PCA was used to analyse differences between the vegetation and forest structure of nesting and random sites. The results indicated a selection for forest stands with larger trees and a higher density of birch trees. Nest sites had higher grass and spleenwort cover. The goshawk avoided habitats characterized by high cover of dwarf shrubs (bilberry, crowberry). Taller shrubs like juniper and raspberry did not appear to influence nest site selection. Distance to power lines and topographical variables did not affect nest site selection either. Goshawks therefore selected nest sites according to criteria partly similar to those described for mixed/coniferous forests – large trees in dense forests – even if what was available differed since birch trees are much smaller than e.g. spruce or pine trees used elsewhere. Forest management in northern Norway should aim at conserving enough areas with this kind of habitat (rich birch forests with tall and dense trees), and disturbance should be avoided in the breeding period as for other birds of prey.